I just posted this answer to the same question (you posted) on Fisheaters:


Both the 1917 Code of Canon Law and the Sacred Congregation of Rites ruled that in an extraordinary situation (e.g., no server), a woman may do the following from outside the sanctuary:

-make all of the responses
-ring the bell

The reasons for this is because neither of these acts are actually intrinsic to the position of the acolyte, such as carrying the candles in procession or ministering the cruets. Also, both acts were added later to the acolyte's duties.

See these articles on my website for further details and citations:

-http://www.romanitaspress.com/articles/dialog_mass.htm (the two articles give the citations from Canon Law and SRC and makes further clarifications)
-http://www.romanitaspress.com/articles/the_altar_bell-part-I.htm

Also, because all Masses are of a public, social nature (even if being offered in a private manner), the Church's attitude has always been that a priest should have (it used to be "must have" unless the priest had been granted a personal indult from the  Holy See, as occurred with Fr. Charles Foucauld, after three years of waiting) a server. If not, then the Church prefers a woman making the responses, etc. to the priest offering Mass alone.

Can not the priest complete the responses by himself?

Yes, Romanitas said that, but that it is preferable to have someone else make them.